The present invention relates to multitrack magnetic recording and reproducing apparatus for recording a variety of information on magnetic tape and reproducing it and also relates to the method of controlling the tracking operation of the multitrack magnetic heads.
Increasing the number of tracks of a conventional multitracking system normally used for recording and reproducing information can improve the fidelity when reproducing the recorded information. However, if such tracks become too dense, the pitches between the tracks become too narrow, thus making it quite difficult to correctly draw out information from individual tracks. The reasons for this are that there is a certain limit to tape-run stability and the relative position of the tape track and the reproducing heads cannot be adequately maintained due to the varying posture of the tape during running. To compensate for this, some systems have introduced a high-precision tape run mechanism for properly regulating tape drift. Nevertheless, such conventional systems still face certain limitations in the realization of complete removal of drift from the running tape. In addition, there is yet another system, the "dynamic tracking control system" that controls the reproducing heads in response to the varying tracking position of these heads during tape run. This system is described below.
FIG. 1 is the typical format of a tracking operation performed by the multi-track magnetic heads of a conventional tracking control system such as it mentioned above. References T1 through Tn respectively indicate the arrangement of magnetic heads dealing with main data tracks containing recorded data on the magnetic tape, such as audio signals, in which the larger rectangles on the left side respectively indicate tracks dealing with the recording magnetic heads and the small rectangles on the right side respectively indicate tracks dealing with the reproducing heads. Reference Tc indicates the arrangement of magnetic heads dealing with the control data track on the magnetic tape, in which the larger rectangles on the left side indicate tracks dealing with the recording magnetic heads and the small rectangles on the right side indicate such tracks dealing with the reproducing heads. As shown in FIG. 1, such a "dynamic tracking control system" is provided with a plurality of magnetic heads H1, H2, - - - Hn and Hc that record signals on the recording tracks T1, T2, - - - Tn and control signals on the tracking control track Tc, while reproducing heads C1, C2 - - - Cn and Cc are in position opposite those recording heads. In addition, a pair of reproducing heads, A and B, are provided for the recording head Hc that records signals on track Hc to enable these heads A and B to follow up the control track Tc by covering the width of the recording head Hc. While following track Tc, the reproducing heads A and B output detect signals Ap and Bp respectively. The relationship between these outputs Ap and Bp against the difference Ap-Bp is shown in FIG. 2. When these reproducing heads A and B are in the positive direction, output Ap from reproducing head A remains constant, whereas output Bp from reproducing head B decreases, and as a result, the difference of outputs Ap31 Bp between reproducing heads A and B increases. Conversely, when the positions of reproducing heads A and B deviate in the negative direction, output Ap from the reproducing head A decreases, whereas output Bp from the reproducing head B remains constant, and thus the difference of outputs Ap-Bp between these heads A and B is led into a negative value. On the other hand, when reproducing head A and B are in normal positions, i.e., in a central position, the difference of outputs Ap-Bp between reproducing heads A and B becomes zero. Applying such functional characteristics described above, the "dynamic tracking control system" corrects the tracking positions of reproducing heads A and B against tracks T1, T2, - - - Tn by using the output differences from these heads as the control signal.
Nevertheless, in addition to the data recording tracks, such a conventional tracking control system still needs to provide a control track for controlling the position of the track reproducing the recorded data signals. And yet, the conventional tracking control system potentially has certain disadvantages described hereafter. When the control signal from the control track is incorrectly transmitted as a result of the dropout of the control signal from the magnetic tape or clogged heads, the reproducing heads cannot be controlled at all. In addition, apart from any such functional problem, even if the positions of the reproducing heads may be corrected by means of control signals delivered from the control track, from the standpoint of functional accuracy, it is technically difficult to correct the height alone i.e., the positions of these heads while maintaining as constant the deviation of the synchronizing signal. In fact, there are definite limits to the achievement of further improvements in the functional accuracy of a conventional tracking control system.